1. Field of the Invention
This invention relates generally to audio/video systems and relates more particularly to delay matching in audio/video systems.
2. Description of the Background Art
Many home theater systems today include a number of audio/video sources connected to an audio/video processor and a video display. For example, the audio/video sources may include a DVD player, a satellite TV receiver, a video game console and the like, for playing content such as a movie. The content from a selected audio/video source is decoded in the audio/video processor to yield an audio portion and a video portion. The audio portion is decoded in the audio/video processor and played through an audio amplifier and a number of audio speakers. The video portion is shown on the video display, which may comprise an analog format television (TV) or a digital format high-definition television (HDTV).
The audio portion and the video portion can be considered as being processed through an audio signal processing path and a video signal processing path in the home theater system. One limitation with the home theater system is that the audio signal processing path and the video signal processing path can have differing delays. For example, the audio signal processing path might have less than three frames of delay and the video signal processing path might have six or more frames of delay (generally, an analog TV has a delay of about 1/60th of a second in the video signal processing path, in comparison with about ⅛th to ⅕th of a second of delay for a digital HDTV). In general, a digital TV has significantly more delay than an analog TV.
Differing delays between the audio signal processing path and the video signal processing path can cause the audio portion of the content and the video portion of the content to become “out of sync” in time (i.e., the audio lagging behind the video, or with the video delayed with respect to the audio). For example, in DVD video playback, an actor's lips may be moving out of sync with his speech, or a gunshot flash and its associated sound may not be coincident in time. As little as 1/30th of a second of time offset between the audio and video portions can generally be detected by a viewer. In a specific example, the viewer can easily detect the actor's lips moving out of sync with his speech if the audio portion leads the video portion by about 25 milliseconds (msec) or more, or if the audio portion lags the video portion by about 80 msec or more. The time mismatch between the audio portion and the video portion can cause significant distraction and dissatisfaction to the viewer.